Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $57.98   3.220%   $59.847   $59.85   $59.85   $59.80  
  Purchase #2 $37.73   8.830%   $41.0616   $41.06   $41.05   $41.10  
  Purchase #3 $62.47   10.128%   $68.797   $68.80   $68.80   $68.80  
  Purchase #4 $60.52   4.537%   $63.2658   $63.27   $63.25   $63.30  
  Purchase #5 $51.60   4.107%   $53.7192   $53.72   $53.70   $53.70  
  Purchase #6 $99.68   12.566%   $112.2058   $112.21   $112.20   $112.20  
  Purchase #7 $202.67   7.394%   $217.6554   $217.66   $217.65   $217.70  
  7 purchase totals = $572.65       $616.5518   $616.57   $616.50   $616.60